The whole thing needs to be redone. He is not trying to pull one over on you here. The whole floor of the shower and pan beneath, and waterproofing system need to come out. The wall tiles and wall waterproofing are tied into this. (Someone else here can give more technical lingo about this than I can.)

A coop unit owner in our building has the same issue, she is refusing to redo the entire shower because she loves the marble walls. The board is having to sue her over it. It is such a train wreck, and of course costing all of us money because it is all of our money that goes to pay the coop’s attorney.

I have successfully replaced shower floors without replacing the walls, however, the homeowner acknowledged that the replaced floor had no guarantee while the replacement floor and walls did. She felt lucky and apparently was as this was a decade ago.

Can you post a pic of your shower? How it is constructed may be instructive.

Since your in a condo and the floor is leaking into the unit below this is already going to cost you plenty with the insurance premiums going up in addition tot he work. Why would you want to take a chance again? Rip the Band-Aid and do it once and do it right. Realistically while you can replace just the floor, you are not really going to be able to tie in the wall waterproofing properly. Again why take the chance.